Lecture 11 - CHO Chemical Analysis Flashcards
True or false: Proximate analysis incorporates CHO
False…. kinda
CHO is not measured directly but instead achieved by subtracting 100% by the summed percentages of moisture, ash, protein, fiber, and fat
what role do CHO play in food?
metabolic energy, if digestible
if not:
- mouthfeel (bulkiness, body, viscosity, stability to emulsions and foams)
- water-holding capacity
- stability to freezing and thawing
- browning
- textures (crispness to smooth, soft gels)
- lower water activity/inhibit microbial growth
how are CHO classified according to WHO and FAO?
size
sugars (DP 1-2)
Oligosaccharides (DP 3-9)
Polysaccharides (DP>9)
how are CHO classified according to international nomenclature rules?
- oligosaccharides = 2-10 (sometimes 20) sugar units
- polysaccharides = 30-60,000 or more monosacch
arabinose is a
monosaccharide
xylose is a
monosaccharide
raffinose is a
trisaccharide
true or false: disaccharides and trisaccharides are considered oligosaccharides
true
list some homopolysaccharides
starch, cellulose, glycogen (only composed of glucose)
list some heteropolysaccharides
pectin, hemicellulose, gums
how are CHO present in foods?
- unbound
- physically associated to other molecules (e.g. starch granules)
- chemically bound (glycolipids, glycol-proteins)
why is CHO determination relevant?
- nutrition labelling
- detection of adulteration
- food quality (sweetness, appearance, stability, texture)
- food processing (affects efficiency)
true or false: proximate analysis is a widely accepted way of determining sugar content in food
nah. it’s erroneous due to experimental errors of any of the other methods. best do it directly.
name the 5 categories of methods used for CHO determination
- chemical
- physical
- enzymatic
- instrumental
- immunoassays
chemical methods include what kind of methods
colorimetric, titration, and gravimetric methods
we got 5 individual methods to memorize from this unit
what are the colorimetric methods of interest eh?
- phenol-sulfuric acid method
- anthrone method
- Somogyi-Nelson Method
what’s the titration method of interest called?
Lane-Enon Method
what’s the gravimetric method of interest called?
Munson-Walker Method
the phenol-sulfuric acid method determines what?
total carbohydrates
describe how the phenol-sulfuric acid method works
1) add sample to H2SO4 under heat
2) furan components are produced
3) add Phenol to induce condensation rxns
4) yellow-gold color is produced
5) measure with spec at 490 nm
the phenol-sulfuric acid method (does/does not) involve stoichiometric reactions
does not
with the phenol-sulfuric acid method, the extent of the reaction is a function of the __________
structure of the sugar
true or false: the phenol-sulfuric acid method is simple, sensitive, accurate, and specific.
true!
with the phenol-sulfuric acid method, what do you do if different sugars are found?
use glucose to prepare a standard curve
true or false: the phenol-sulfuric acid method can also be used to determine sugar alcohols
false. does not produce a positive result
the Anthrone method measures what?
total carbohydrate
describe the Anthrone method
- CHO are dehydrated by strong acids to produce a furan component
- furan components react with Anthrone reagent
- blue green color formed
- measure abs at 620 nm
draw the structure of HMF (hydroxymethylfurfural)
yikes okay (looks like someone squared up)
Fehling’s test measures what?
presence of aldehydes
describe Fehling’s test
- copper II is reduced to copper oxide
- this shifts color from blue to brick red
Reagents:
A: CuSO4*H20 in d-water with 2 drops of dilute sulfuric acid
B: Potassium tartrate and NaOH in d-water
what’s the somogyi-nelson method?
fehling’s method: who are you?
somogyi-nelson method: i’m you but better
uses enzymes before addition of reagent so oligo and polysaccharides can be determined
somogyi-nelson method measures what?
reducing sugars
describe the somogyi-nelson method
Reagents:
- NaOH
- CuSO4
- ammonium molybdate
- sodium arsenate
(the last 2 form an arsenomolybdate complex)
1) solution of Cu2SO4 and NaOH is added to solution of reducing sugars
2) mixture heated in boiling water bath
3) add the other 2 reagents
4) arsenomolybdate complex is reduced by Cu(I) to a stable blue color
5) measure @ 520 nm with spec
Lane & Eynon method measures what?
reducing sugars
the Lane & Eynon method is based on the _____ action of CHO toward certain _____ _____
reducing; metallic salts
describe the Lane & Eynon method
- titrate CHO against known concentration of CuSO4 in alkaline condition
- use methylene blue as indicator
- end point indicated by solution turning colorless
true or false: the Lane & Eynon method can directly determine concentration of non-reducing sugars
false
limits of the Lane-Eynon method?
- results depend on precise reaction times. conditions must be controlled (temp, reagent concentrations)
- can’t distinguish between types of reducing sugars
- can’t directly determine concentration of non-reducing sugars
- susceptible to reducing molecules
The Munson & Walker method measures what?
reducing sugars
describe the Monson & Walker method
- Sample w/reducing sugar is introduced to CuSO4, base, and heat
- oxidized sugar plus CuO2 precipitate is formed
- weigh precipitate
amount of precipitate is directly related to concentration of reducing sugars in sample
limits of the Munson & Walker method?
(same as Lane & Eynon)
- depends on precise rxn times
- can’t distinguish between different types of reducing sugars
- can’t directly determine concentration of non-reducing sugars
- susceptible to interference from other reducing molecules
which method is more reproducible and accurate? Lane & Eynon or Munson & Walker?
Munson & Walker
limits of the phenol-sulfuric acid method?
- requires clear solution
- standard curve must be made with same exact mixture of CHO, ratios and all that occur in the sample
what do you do if there’s interfering reducing compounds for your reducing sugar methods?
extract em
